Isomerization of normal pentane



my H95@ B. H. GWYNN ET AL 539,

ISOMERIZATION OF NORMAL PENTANE Filed Dec. 18, 1946 BERNJZRD 1H. C-INVYNNl CHRLES W. MOJYTGOMERY Patented Nov. 2l, i950 UNITED STATES ISUMEREZATEON F NUR/MAL PENTANE Bernard H. Gwynn, Tarentum, and Charles W. Montgomery, Galimcnt, Pa., assignors to Gulf Research t Eeveloprnent Company, Pittsburgh, Pa., a corporation of Delaware Application December 4llS, 1946, Serial No. '717,010

(Cl. 26d-683.5)

l 3 Claires.

This invention relates to the isomerization oi normal pentane, and it is particularly concerned with an improved process of producing .isopentane from normal pentane with a minimum amount of cracking.

Catalytic pentane isomerization processes have heretofore been proposed wherein increased yields of isopentane have been obtained byV employing various cracking inhibitors, such as benzene, naphthenes, hydrogen, propane, and butanes. These processes reduire high isomerizy ing temperatures which, in turn, require high pressures, thus introducingl into the process the vdiiculties accompanying high temperature-high pressure operation, and they introduce into the process undesirable materials which must subsequently be removed.

It is an object achieved by this invention to provide an improved pentane isomerization process in which increased yields of isopentane are obtained.

Another object achieved by this invention is to provide an improved process for the isomerizaion of normal pentane at relatively low temperatures in which a product consisting essentially of normal and isopentanes is obtained without resorting to fractionation for the seperation of a cracking inhibitor.

A further object achieved by this invention is to provide an improved pentane isomerization process in which the formation oi aluminum halide-hydrocarbon complexes is minimized and improved use is made of the catalytic activity of the aluminum halide.

Other objects achieved by this invention will become apparent in the following detailed description thereof.

We have discovered that increased yields of isopentane can be obtained during the isornerizavtion of normal pentane in the presence of an aluminum halide catalyst and a hydrogen halide promoter if a predetermined amount oi isopentane is introduced with the normal pentane to be isomerized. For example, we have found that isopentane yields above about 50 per cent can be obtained if the normal pentane to be iso merized is mixed with isopentane in an amount corresponding to about 33 to about .50 per cent by weight of the mixture. lf less than about 33 per cent or more than about 50 to 52 per cent by weight of isopentane is present initially in the normal pentane feed, the yield of isopentane is less than the yield without the presence of anyy initial isopentane. Particularly good yields ci isopentane are produced without substantial cracking if the proportion of isopentane in the pentane feed is maintained at between about 35 per cent and about ll5 per cent by weight of the total hydrocarbons present and best yields are obtained with an initial isopentane concentration of about 40 to 41 per cent. Also, we have found that for the greatest efciency the reaction mixture withdrawn from the reaction zone should contain not more than about per cent by Weight of isopentane. The process can be operated to give greater than about 60 per cent of isopentane, but when greater than about 60 per cent of isopentane is obtained in the product stream, there also are obtained considerable amounts of cracking and decomposition products with accompanying side reactions and deterioration of the catalyst taking place. Accordingly, when the product stream contains more than about 60 per cent by weight oi isopentane, the advantage gained by the initial isopentane concen tration is oiset by the formation of side reaction products. The process of our invention, is therefore, most advantageously carried out'with an initial isopentane concentration of about 40 to 4l per cent and a final isopentane concentration not greater than about 60 per cent. The conversion or normal pentane to isopentane taking place during a single pass through the reactor is relatively small; however, the circulation rate is sufciently fast togive a commercially attrac, tive process.

The vyield of isopentane referred to herein is a measure of the eiciency of the conversion of normal pentane to isopentane and is calculated by dividing the mols of isopentane formed by the mols of normal pentane converted, all multiplied by 100.

The catalyst used in carrying out the process of our invention can be an aluminum halide, such as` aluminum chloride or aluminum bromide. These halides can be used alone or in combination with a carrier or support material, such as zeolites, permutites, and the like. If desired, the aluminum halide can be suspended or dissolved `in an inert liquid or can be reacted with unsaturated hydrocarbons to form active aluminum halide-hydrocarbon complexes.

The isomerization can be effected over a wide range of space velocities. In general, space velocities of from about 9.1 to 4 or 5 volumes of liquid feed per volume of catalyst per hour are employed.

The promoter used to increase the activity of the aluminum halide catalyst in accordance with our invention can be a hydrogen halide, such as hydrogen chloride or hydrogen bromide. The amount of hydrogen halide used is not particularly critical; however, we advantageously use an amount corresponding to between about 2 and about 4 per cent by weight based on the weight of the hydrocarbons present in the reaction zone. We have found that if less than about 2 per cent by weight of a hydrogen halide is used, the rate of normal pentane conversion drops olf rapidly, and that if more than about 4 per cent of a hydrogen halide is used, the amount of cracking increases rather rapidly.

The process of our invention is executed at a temperature below about '70 C. and preferably at a temperature within the range of about 40 C. to about 60 C. In general, temperatures higher than about 70 C. are not suitable because at these temperatures the isomerization reaction is accompanied by increased cracking and other decomposition reactions. The minimum temperature at which our invention may be practiced depends upon whether the process is being carried out in the liquid phase or the vapor phase. Our process can be carried out in the liquid phase at a temperature less than 40 C., but from a commercial standpoint, the temperature is advantageously above about 40 C. If a highly active catalyst and promoter are used, We may employ temperatures even as low as 25 C. Vapor phase isomerization naturally must be carried out above the boiling point of normal pentane. Liquid phase isomerization is carried out under a pressure sufficient to maintain the reactants in liquid phase. A pressure of 200 pounds per square inch or less should be adequate to maintain the reactants in the liquid phase at a temperature of '70 C. or less.

Our invention may be applied to isomerization of normal pentane in liquidv phase, vapor phase, and mixed liquid-vapor phase; however, our invention is most advantageously applied to liquid phase isomerization because of certain economic advantages obtained by liquid phase isomerization; Therefore, while our invention is hereinafter described in connection with its preferred embodiment, liquid-phase isomerization, it isalso within the scope of our invention to carry out the isomerization process in vapor phase and mixed liquid-vapor phase.

Our invention is particularly advantageous in that no diluent is introduced into the reaction mixture. Accordingly, the processor our invention is economical in that fractionation of a diluent cracking inhibitor is avoided. When our process is carried out according to its preferred embodiment, the product from the reaction zone consists essentially of pentanes. The concentration of isopentane in the reaction product is of the order of 50-60 per cent by weight. The reaction product may then be treated according to several schemes. According to one plan, illustrated schematically in the figure, a portion of the product from the reaction zone is mixedl with normal pentane feed. The proportion of reaction product to normal pentane feed is adjusted to give a mixture containing between about 33 and about 50 per cent by weight of isopentane. The portion of the reaction product not mixed with normal pentane feed is freed from catalyst and promoter and is then fractionated to give an isopentane fraction and a normal pentane fraction, which latter fraction is recycled to the beginning of the process.

An alternate procedure to the above plan would be to omit the fractionation step and to recover a normal pentane-isopentane fraction which could be used per se as a blending stock.

A further scheme would be to fractionate the entire reaction product into an isopentane fraction and a normal pentane fraction, in which case the normal pentane fraction could be recycled to the beginning of the process and the isopentane fraction could be divided into two portions, one portion of which could be recycled tothe beginning of the process as cracking inhibitor and the second portion could be withdrawn to storage.

Now referring to the gure, liquid normal pentane from an outside source is introduced through valve i and conduit II into conduit I2 where it is mixed with normal pentane recycle withdrawn from the bottom of fractionator i5 through conduit 9, valve 50 and conduit 5I. The pentane feed then passes into conduit I3 where it is mixed with hydrogen chloride from conduit I4 and product stream from conduit It containing not more than about per cent by weight of isopentane. The hydrogen chloride in conduit Ii consists of fresh hydrogen chloride introduced through conduit I5 and valve IE and recycle hydrogen chloride introduced through conduit Il and valve I8. The product stream enters conduit I3 from conduit I9 containing valve 20. From conduit I3 the pentane-hydrogen chloride solution enters pump 2I through conduit 22. The-pentane-hydrogen chloride solution is then pumped into conduit 23, from which a major proportion is circulated by pump 2| through conduit 2li containing valve 25 to conduit 22. A minor proportion of the pentane-hydrogen chloride solution from conduit 23 is withdrawn through valve 26 and conduit 2l into the lower portion of reactor 28 which is advantageously maintained at a temperature of 40 to 60 C.

The circulation of a major proportion of the pentane-hydrogen chloride solution through conduit 2Q- insures thorough mixing of the normal pentane introduced through conduit I2 with the hydrogen chloride and the isopentane-containing product stream introduced through conduits Ill and i8, respectively. By this mixing procedure the isopentane in the product recycle stream is thoroughly mixed with the incoming pentane prior to its introduction into the reactor so that no charge containing less than about 33 per cent of isopentane can come in contact with the catalyst. Thorough mixing of the isopentane with the normal pentane is necessary in order to avoid local decomposition reactions which would other- Wise occur near the point of feed in the reactor.

Only one reactor is shown in the figure; lio-wever, continuous operation may require several reactors so that when the catalyst in one reactor is reduced below an economic operating level, the now can be diverted to another reactor while the depleted reactor is being recharged with fresh catalyst. Reactor 28 may contain solid aluminum chloride or aluminum chloride deposited on a suitable support or it may contain one of the various liquid catalysts wherein aluminum chloride is dissolved, suspended, or reacted with some organic or inorganic material. Reactor 28 may be provided at its top with a plate 29 which can be removed when it is necessary to charge the reactor with fresh solid catalyst. The reactor may also be provided at its bottom with a conduit 35i and valve 3l through which catalyst sludge, if formed, may be withdrawn or through 5. tion of the normal pentane is isomerized to isopentane so that the resulting product stream contains not more than about 60 per cent isopentane. The concentration of isopentane in the incoming stream is maintained between about 33 per cent and about 50 per cent. The upper portion of reactor 28 is provided with a settling zone 32 to minimize catalyst carry-over into product and recycle lines. From the top of settling zone 32 a product stream containing not more than about 60 per cent of isopentane is withdrawn through conduit 33. One portion of the pro-duct stream is Vrecycled through valve and conduit I9 to conduit i3 wherein it is mixed with a predetermined quantity of normal pentane so that vthe resulting mixture contains less thanabout per cent but more than 33 per cent of isopentane. The portion of the product stream not recycled through conduit I9 passes from conduit 33 through conduit 34 anfi valve 35 into separator 36 where any entrained catalyst is settled out. The amount of product stream removed through conduit 34 is controlled by valve 35 so that the isopentane concentration at the top of the reactor does not exceed about 60 per cent. From the bottom of separator 35, settled catalyst is periodically withdrawn by means of valve 3? thro-ugh conduit 38. If desired, the settled catalyst can be recycled to reactor 20. From the top of separator 38, a product stream is removed through conduit 39 to hydrogen chloride stripper lill. From the top of hydrogen chloride stripper 40, hydrogen chloride and non-condensible gases are removed through conduit 4l and recycled in part through conduit Il to the beginning of the process. A portion of the hydrogen chloride recycle may be removed by valve 42 through conduit 43 to prevent light hydrocarbon gases that might be formed from building up in the system. From the bottom of hydrogen chloride stripper 4i), a liquid product is removed through valve and conduit 44 to a fractionator 45 wherein the isopentane is fractionated and removed as an overhead product through conduit 45. From the bottom of fractionator 45 normal pentane is withdrawn through conduit 49 and recycled through valve and conduit 5! to the beginning of the process. If, before the process gets on stream, an excess of hexanes or heavier hydrocarbons is formed, all or a portion of thenormal pentane may be withdrawn from conduit 49 through valve 52 and conduit 53 and then subjected to fractionation to remove the hexanes or heavier hydrocarbons before returning the normal pentane to the beginning of the process. Likewise, if butanes are formed, all or a portion of the stream coming froml the bottom of hydrogen chloride stripper 4c may be subjected to debutanization before entering fractionator 45. If a product consisting essentially of normal and isopentanes is desired for use as a blending stock,

fractionator 45 is cut out of the system by closing valve 54 and opening valve 4l. The mixture of pentanes is then withdrawn through conduit 4S to storage or to a blending plant for additional handling.

In continuous operation, reactor 28 containing an aluminum halide catalyst is advantageously lled at the start of a run with a mixture consisting of about 40 per cent isopentane and about per cent normal pentane. The reactor is then heated to about 50 C. and a normal pentaneisopentane-hydrogen chloride solution containing at least 33 per cent and not more than 50 per cent of isopentane and 2 to 4 per cent of hydrogen valve 35 so that the isopentane concentration is not in excess of about 60 per cent. For example, if 20 parts of a 50-50 mixture of normal pentane and isopentane is withdrawn through conduit 34, 20 parts of normal pentane enter the system through conduit I2. The 20 parts of normal pentane introduced by conduit I2 may consist of 10 parts of fresh normal pentane entering through conduit II and 10 parts of recycle normal pentane coming from the bottom of fractionator 49 through valve 50 and conduit 5I. For every 20 parts of normal pentane entering through conduit I2, parts of the 50-50 mixture of normal pentane-isopentane is recycled through conduit I9, to conduit I3 wherein it meets the normal pentane charge. Thorough mixing is obtained by the charge circulating through conduit 22, pump 2i, conduit 23, and conduit 24 containing valve 25. After thorough mixing has been obtained, the feed hydrocarbons enter the lower portion of reactor 28 in the proportion of about 50 parts of isopentane per 70 parts of normal pentane. The isopentane concentration in the mixture accordingly is about 41.5 per cent.

The following is given as illustrative of the present invention, but it is to be understood that the invention is not restricted thereto. The following runs were carried out to determine the effect of varying the percentage of isopentane in the charge for normal pentane isomerization. In each of the runs 50 mls. of normal pentane or 50 mls. of a mixture of normal pentane and isopentane was placed in a stainless steel bomb of approximately 100 mls. capacity. To the pentane charge there was added 7.4 grams of anhydrous aluminum chloride. The bomb was closed and then immersed in a Dry Ice-acetone bath. When the bomb and its contents reached the approximate temperature of the Dry Ice bath, 0.6 gram, or about 2 per cent by weight of the hydrocarbons charged, of anhydrous hydrogen chloride was added to the reaction mixture. The bomb was then attached to agitating means and immersed in a bath maintained at a temperature of 48.6 C. After remaining in the constanttemperature bath for 45 minutes with continual agitation, the bomb was removed and quickly chilled in a Dry Ice-acetone bath. The bomb was then opened, the contents decanted and fractionated. The following table shows the effect of varying the concentration of isopentane initially present. It will be noted that with respect to the per cent yield the concentration of isopentante initially present in the charge is a critical fac or.

Table Run Run Run Run Run Run l 3 4 5 6 Charge. wt. per cent:

n-pcntane 99.0 79. 7 68.2 G5. 0 55.0 51.4 isopentane 1. 0 20. 3 31. 8 35.0 45.0 48. 6 Analysis, wt. per cen isobutane 21.9 20.2 15.5 l 2 0.5 2.4 n-butaneisopentanc 30. 5 34. 4 43. 7 48. 8 54. 'i 59. 7 n-pentane 28.1 31.0 29. 3 47. 1 44. 0 33. 1 hexane-- 19. 5 14. 4 1l. 5, 2. 9 1.2 4. 8 Yield, per cent 1 4l. 5 29.0 30. 6 77. 2 84. 5 60. 7

1 mols isopentane formed X100 mols npentane converted The above.y results show the criticality or controlling the proportion of isopentane initially present. It. will be noted that in run 1 wherein only 1 per cent of isopentane was initially present, a yield of 41.5 per cent resulted. It can be noted from runs 2 and 3 wherein more than 1 per cent but less than 33 per cent of isopentane was present that the yield was even less than the yield of run 1. In runs 4, 5, and 6, however, wherein the initial isopentane concentrations were 35, 45 and 48.6, respectively, the yields were 77.2, 84.5, and 60.7, respectively. Yields even above 84.5 per cent may be obtained by proper control of' the initial isopentane concentration. It will be noted from all of the runs that the concentration of isopentane in the product stream is less than 60 percent. We have found that if more than about 60 per cent of isopentane is obtained in the product stream, the efficiency, or asv referred to herein the yield, of isopentane is less.

This invention has been described with particular reference to certain embodiments and specific examples, but it is not limited to such embodiments or examples except as dened in the appended claims.

We claim:

1. In a process oi producing isopentane from normal pentane by contacting normal pentane with an aluminum halide catalyst in the presence of a hydrogen halide under isomerizing conditionsl and in the absence or" a cracking inhibitor other than that specified below, the improvement comprising contacting with said aluminum halide and hydrogen halide in a reaction zone at a temperature below about 79 C. a charge mixture consisting essentially or normal pentane andY isopentane, said charge-mixture containing about 85` to about 45 per cent by weight of isopentane, said isopentane acting to inhibit cracking of said normal pentane, and withdrawing from said reaction zone a reaction mixture containing substantially more isopentane than was present initially and not more than about 60 per cent by weight oisopentane.

2. In a process of producing isopentane from normal pentane by contacting normal pentane with an aluminumY halide catalyst in the presence of a hydrogen halide under isomerizing conditions and in the absence of a cracking inhibitor other than that specified below, the improvement comprising contacting with said aluminum halide and hydrogen halide in a reaction zone at a temperature below about 70 C. a charge mixture consisting essentially of liquid normal pentane and isopentane, said charge mixture containing about 35 to about 45 per cent by weight of isopentane, said isopentane acting to inhibit cracking of said normal pentane, and withdrawing from said reaction Zone a reaction mixture containing substantially more isopentane than was present initially and not more than about per cent by Weight of isopentane.

3. In a process of producing isopentane from normal pentane by contacting normal pentane with an aluminum halide catalyst in the presence of a hydrogen halide promoter under isomerizing conditions in the absence of a cracking inhibitor other than that specified below, the improvement comprising contacting with said aluminum halide and hydrogen halide in a reaction zone at a temperature below about C. a charge mixture consisting essentially of normal pentane and isopentane, said charge mixture containing about 35 per cent to about 45 per cent by weight 0f isopentane, said isopentane acting to inhibit cracking of said normal pentane, withdrawing from said reaction zone a reaction mixture containing substantially more isopentane than was present initially and not more than about 60 per cent by weight of isopentane, dividing said reaction mixture into two portions, recycling to the beginning of the process one of said portions admixed with normal pentane in an amount sufficient to produce a charge mixture consisting essentially of normal pentane and isopentane and containing between about 35 per cent and about 45 per cent by weight of isopentane, and separately recovering the remaining portion.

BERNARD H. GWYNN. CHARLES W. MONTGOMERY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,334,553 Harding Nov. 16, 1943 2,353,098 Whiteley et al. July 4, 1944 2,408,543 Bloch Oct. 1, 1946 2,433,079 Whiteley et al Dec. 23, 1947 2,439,301 Hudson et al Apr. 6, 1948 2,443,607 Evering June 22, 1948 

1. IN A PROCESS OF PRODUCING ISOPENTANE FROM NORMAL PENTANE BY CONTACTING NORMAL PENTANE WITH AN ALUMINUM HALIDE CATALYST IN THE PRESENCE OF A HYDROGEN HALIDE UNDER ISOMERIZING CONDITIONS AND IN THE ABSENCE OF A CRACKING INHIBITOR OTHER THAN THAT SPECIFIED BELOW, THE IMPROVEMENT COMPRISING CONTACTING WITH SAID ALUMINUM HALIDE AND HYDROGEN HALIDE IN A REACTION ZONE AT A TEMPERATURE BELOW ABOUT 70*C. A CHARGE MIXTURE CONSISTING ESSENTIALLY OF NORMAL PENTANE AND ISOPENTANE, SAID CHARGE MIXTURE CONTAINING ABOUT 35 TO ABOUT 45 PER CENT BY WEIGHT OF ISOPENTANE, SAID ISOPENTANE ACTING TO INHIBIT CRACKING OF SAID NORMAL PENTANE, AND WITHDRAWING FROM SAID REACTION ZONE A REACTION MIXTURE CONTAINING SUBSTANTIALLY MORE ISOPENTANE THAN WAS PRESENT INITIALLY AND NOT MORE THAN ABOUT 60 PER CENT BY WEIGHT OF ISOPENTANE. 